This patch is taken from debian's glibc package (generate-supported.mk).
It install the localedata/SUPPORTED file of the glibc. This file lists
all the supported locales of the glibc.

diff --git a/localedata/Makefile.old b/localedata/Makefile
index 34877c0..a61d9b9 100644
--- a/localedata/Makefile.old
+++ b/localedata/Makefile
@@ -91,7 +91,8 @@ endif
 # Files to install.
 install-others := $(addprefix $(inst_i18ndir)/, \
 			      $(addsuffix .gz, $(charmaps)) \
-			      $(locales))
+			      $(locales)) \
+                   $(inst_i18ndir)/SUPPORTED
 
 tests: $(objdir)/iconvdata/gconv-modules
 
@@ -195,6 +196,14 @@ endif
 
 include SUPPORTED
 
+$(inst_i18ndir)/SUPPORTED: SUPPORTED $(+force)
+	for locale in $(SUPPORTED-LOCALES); do \
+		[ $$locale = true ] && continue; \
+		echo $$locale | sed 's,/, ,' >> LOCALES; \
+	done
+	$(make-target-directory)
+	$(INSTALL_DATA) LOCALES $@
+
 INSTALL-SUPPORTED-LOCALES=$(addprefix install-, $(SUPPORTED-LOCALES))
 
 # Sometimes the whole collection of locale files should be installed.
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<div class='path'>path: <a href='/guix/log/?id=0d53223c814e33bd5b45bf15907953e36e97066a'>root</a>/<a href='/guix/log/gnu?id=0d53223c814e33bd5b45bf15907953e36e97066a'>gnu</a>/<a href='/guix/log/gnu/tests.scm?id=0d53223c814e33bd5b45bf15907953e36e97066a'>tests.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/tests.scm?id=0d53223c814e33bd5b45bf15907953e36e97066a&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2022-05-18 22:29:54 +0200'>2022-05-18</span></td><td><a href='/guix/commit/gnu/tests.scm?id=9a5d68692314bebd16dbcdc0d4e4e52fa4d5812f'>services: Add more description fields.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-08-29 01:05:26 -0400'>2021-08-29</span></td><td><a href='/guix/commit/gnu/tests.scm?id=da4e40948326387d5bcda58783914d5f9ce8b095'>Migrate to the new 'targets' field of bootloader-configuration.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-04-12 18:42:22 +0200'>2021-04-12</span></td><td><a href='/guix/commit/gnu/tests.scm?id=3332f4365bf329c361d650c70e53b8a74ad923bd'>tests: Support package extensions in the backdoor REPL.</a><span class='msg-avail'>...</span></td><td>Maxime Devos</td></tr>
<tr><td><span title='2021-02-19 20:10:08 +0100'>2021-02-19</span></td><td><a href='/guix/commit/gnu/tests.scm?id=f57b7cea748c1e8284373811c13398d9f69aec89'>tests: Export %simple-os.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2020-07-25 19:11:36 +0200'>2020-07-25</span></td><td><a href='/guix/commit/gnu/tests.scm?id=a5e2fc73760a2ae023f2e56bdbf8025971f90e64'>utils: Move &lt;location&gt; and '&amp;error-location' to (guix diagnostics).</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-03-05 16:33:37 +0100'>2020-03-05</span></td><td><a href='/guix/commit/gnu/tests.scm?id=c0b726c2112e0e670dc134583b376541c0a3789a'>tests: Add &lt;system-test&gt; gexp compiler.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-01-23 11:26:55 +0100'>2020-01-23</span></td><td><a href='/guix/commit/gnu/tests.scm?id=f79313b3871ebe204c7b29fdb823666af06f48ff'>tests: Fix typo in comment.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-12-18 22:36:37 +0100'>2019-12-18</span></td><td><a href='/guix/commit/gnu/tests.scm?id=ab7010af1f1077c056529769a53a380147c3933f'>gexp: Allow character literals in GEXP-&gt;SEXP.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2019-09-23 23:41:19 +0200'>2019-09-23</span></td><td><a href='/guix/commit/gnu/tests.scm?id=7abd5997f41fec38ea1daa9099a9693062f10dbc'>repl, marionette: 'self-quoting?' matches keywords.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>